July 2012
Volume 53, Issue 8
Free
Letters to the Editor  |   July 2012
The Association between Glaucoma Prevalence and Supplementation with the Oxidants Calcium and Iron
Author Affiliations & Notes
  • Yahya Shaikh
    Harbor-UCLA Medical Center, Los Angeles, California;
  • Fei Yu
    Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California; and the Departments of
    Biostatistics and
  • Anne L. Coleman
    Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California; and the Departments of
    Epidemiology, Jonathan and Karin Fielding School of Public Health, UCLA, Los Angeles, California.
Investigative Ophthalmology & Visual Science July 2012, Vol.53, 4941-4942. doi:10.1167/iovs.12-10315
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Yahya Shaikh, Fei Yu, Anne L. Coleman; The Association between Glaucoma Prevalence and Supplementation with the Oxidants Calcium and Iron. Invest. Ophthalmol. Vis. Sci. 2012;53(8):4941-4942. doi: 10.1167/iovs.12-10315.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Introduction
We read with interest the article by Wang et al. 1 in the February issue, in which they used self-reported glaucoma in the National Health and Nutrition Examination Survey (NHANES) population to find an association between the prevalence of glaucoma and the highest quintiles of the intake of calcium and iron supplementation. When we tried to replicate their analysis using the same NHANES 2007 and 2008 data, we noticed that there might be typos in quintiles of supplemental calcium and iron intake in their report, as shown in Table 1
Table 1. 
 
Quintiles of Supplemental Calcium and Iron Intake in the 2007 and 2008 NHANES Data
Table 1. 
 
Quintiles of Supplemental Calcium and Iron Intake in the 2007 and 2008 NHANES Data
Quintiles of Supplemental Calcium and Iron Intake Reported in Wang et al.1 Quintiles of Supplemental Calcium and Iron Intake Used to Replicate Results in Wang et al.1
Calcium Calcium
 No intake  No intake
 1st Quintile, >0 and
 <100 mg/day
 1st Quintile, >0 and
 ≤100 mg/day
 2nd Quintile, ≥100 and
 <200 mg/day
 2nd Quintile, >100 and
 ≤200 mg/day
 3rd Quintile, ≥200 and
 <375 mg/day
 3rd Quintile, >200 and
 ≤375 mg/day
 4th Quintile, ≥375 and
 <800 mg/day
 4th Quintile, >375 and
 ≤800 mg/day
 5th Quintile,
 ≥800 mg/day
 5th Quintile,
 >800 mg/day
Iron Iron
 No intake  No intake
 1st Quintile, >0 and
 <6 mg/day
 1st Quintile, >0 and
 ≤6 mg/day
 2nd Quintile, ≥6 and
 <15 mg/day
 2nd Quintile, >6 and
 ≤15 mg/day
 3rd Quintile, ≥15 and
 <18 mg/day
 3rd Quintile, >15 and
 ≤18 mg/day
 4th and 5th Quintiles,
 ≥18 mg/da
 4th and 5th Quintiles,
 >18 mg/day
In addition, our analyses of the same NHANES data do not support the statement by the authors that “there is no compelling reason to believe that individuals taking a high level of supplementary oxidants would be systematically more or less likely to accurately recall a glaucoma diagnosis than would those taking lower levels of such supplementation.” In our analyses, a clinical diagnosis of glaucoma was defined as (1) having either two or more abnormal points in at least one eye on the frequency doubling threshold tests (N30-5 FDT) on two tests in the same eye 2,3 along with a cup-to-disc ratio (CDR) in at least one eye on the optic disc photographs or CDR asymmetry between eyes of the same subject of ≥97.5th percentile of the normal NHANES population, or (2) having a CDR or CDR asymmetry between eyes of the same subject of ≥99.5th percentile of the normal NHANES population among subjects who did not have complete FDT results, 4 after excluding subjects who had a documented alternative explanation for CDR findings (dysplastic disc or marked anisometropia) or for the visual field defect (retinal vascular disease, macular degeneration, or cerebrovascular disease). 4 Based on this definition, 36% of 72 subjects who self-reported having glaucoma had a clinical diagnosis of glaucoma. Interestingly, individuals who did not report themselves as having glaucoma were less likely to report the supplemental intake of calcium and iron whether or not they had a clinical diagnosis of glaucoma. For example, 27.5% and 28.3% of those without self-reported glaucoma and with and without a clinical diagnosis of glaucoma, respectively, took calcium supplementation >200 mg/day versus 39.0% and 43.8% of those with self-reported glaucoma and with and without a clinical diagnosis of glaucoma, respectively, who took calcium supplementation >200 mg/day. The same trends were seen with supplemental iron intake (Table 2). 
Table 2. 
 
Percentages of Supplemental Nutrient Intake among Participants in NHANES 2007 and 2008 with and without Self-Reported Glaucoma and Clinical Diagnosis of Glaucoma*
Table 2. 
 
Percentages of Supplemental Nutrient Intake among Participants in NHANES 2007 and 2008 with and without Self-Reported Glaucoma and Clinical Diagnosis of Glaucoma*
Supplemental Calcium and Iron Intake Self-Reported Glaucoma with Clinical Diagnosis of Glaucoma (n = 31) Self-Reported Glaucoma without Clinical Diagnosis of Glaucoma (n = 41) No Self-Reported Glaucoma with Clinical Diagnosis of Glaucoma (n = 111) No Self-Reported Glaucoma without Clinical Diagnosis of Glaucoma (n = 1857)
Calcium
 No intake 49.9 25.9 50.5 48.3
 1st Quintile, >0 and ≤100 mg/day 4.5 27.7 7.9 12.0
 2nd Quintile, >100 and ≤200 mg/day 6.6 2.6 14.1 11.5
 ≥3rd Quintile, >200 mg/day 39.0 43.8 27.5 28.3
Iron
 No intake 74.4 76.3 83.4 78.7
 1st Quintile, >0 and ≤6 mg/day 0 3.3 1.2 4.5
 2nd Quintile, >6 and ≤15 mg/day 3.8 1.5 5.1 5.2
 ≥3rd Quintile, >15 mg/day 21.7 18.9 10.3 11.7
Furthermore, in our evaluation of the serum levels of calcium and iron instead of the self-report of supplemental calcium and iron intake, there were no statistically significant associations between self-reported glaucoma and highest quintiles of albumin-corrected serum calcium (odds ratio [OR] 1.1, 95% confidence interval [CI] 0.7–1.7), serum iron (OR 1.6, 95% CI 0.9–2.7), or serum ferritin (OR 2.0, 95% CI 0.1–31.6) in the fully adjusted (age, sex, ethnicity, socioeconomic status, comorbidities, and general health condition) logistic regression models. Similarly, there were no statistically significant associations between clinical diagnosis of glaucoma and highest quintiles of albumin-corrected serum calcium (OR 1.0, 95% CI 0.4–2.2), serum iron (OR 0.7, 95% CI 0.4–1.5), or serum ferritin (OR 0.1, 95% CI 0.005–1.8) in the fully adjusted logistic regression models. 
The above findings suggest that the knowledge of a glaucoma diagnosis may drive supplement use, as is found in other diseases, 57 and that the use of self-report for a diagnosis of glaucoma as an outcome should be done cautiously. In addition, there was no statistically significant association between the serum levels of calcium, iron, or ferritin and the clinical diagnosis of glaucoma. 
References
Wang SY Singh K Lin SC. The association between glaucoma prevalence and supplementation with the oxidants calcium and iron. Invest Ophthalmol Vis Sci . 2012;53:725–731. [CrossRef] [PubMed]
Quigley HA. Identification of glaucoma-related visual field abnormality with the screening protocol of frequency doubling technology. Am J Ophthalmol . 1998;125:819–830. [CrossRef] [PubMed]
Spry PG Hussin HM Sparrow JM. Performance of the 24-2-5 frequency doubling technology screening test: a prospective case study. Br J Ophthalmol . 2007;91:1345–1349. [CrossRef] [PubMed]
Foster PJ Buhrmann R Quigley HA Johnson GJ. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol . 2002;86:238–242. [CrossRef] [PubMed]
Velentzis LS Keshtgar MR Woodside JV Significant changes in dietary intake and supplement use after breast cancer diagnosis in a UK multicentre study. Breast Cancer Res Treat. 2011;128:473–482. [CrossRef] [PubMed]
Velicer CM Ulrich CM. Vitamin and mineral supplement use among us adults after cancer diagnosis: a systematic review. J Clin Oncol . 2008;26:665–673. [CrossRef] [PubMed]
Rock CL. Multivitamin-multimineral supplements: who uses them? Am J Clin Nutr . 2007;85:277S–279S. [PubMed]
Table 1. 
 
Quintiles of Supplemental Calcium and Iron Intake in the 2007 and 2008 NHANES Data
Table 1. 
 
Quintiles of Supplemental Calcium and Iron Intake in the 2007 and 2008 NHANES Data
Quintiles of Supplemental Calcium and Iron Intake Reported in Wang et al.1 Quintiles of Supplemental Calcium and Iron Intake Used to Replicate Results in Wang et al.1
Calcium Calcium
 No intake  No intake
 1st Quintile, >0 and
 <100 mg/day
 1st Quintile, >0 and
 ≤100 mg/day
 2nd Quintile, ≥100 and
 <200 mg/day
 2nd Quintile, >100 and
 ≤200 mg/day
 3rd Quintile, ≥200 and
 <375 mg/day
 3rd Quintile, >200 and
 ≤375 mg/day
 4th Quintile, ≥375 and
 <800 mg/day
 4th Quintile, >375 and
 ≤800 mg/day
 5th Quintile,
 ≥800 mg/day
 5th Quintile,
 >800 mg/day
Iron Iron
 No intake  No intake
 1st Quintile, >0 and
 <6 mg/day
 1st Quintile, >0 and
 ≤6 mg/day
 2nd Quintile, ≥6 and
 <15 mg/day
 2nd Quintile, >6 and
 ≤15 mg/day
 3rd Quintile, ≥15 and
 <18 mg/day
 3rd Quintile, >15 and
 ≤18 mg/day
 4th and 5th Quintiles,
 ≥18 mg/da
 4th and 5th Quintiles,
 >18 mg/day
Table 2. 
 
Percentages of Supplemental Nutrient Intake among Participants in NHANES 2007 and 2008 with and without Self-Reported Glaucoma and Clinical Diagnosis of Glaucoma*
Table 2. 
 
Percentages of Supplemental Nutrient Intake among Participants in NHANES 2007 and 2008 with and without Self-Reported Glaucoma and Clinical Diagnosis of Glaucoma*
Supplemental Calcium and Iron Intake Self-Reported Glaucoma with Clinical Diagnosis of Glaucoma (n = 31) Self-Reported Glaucoma without Clinical Diagnosis of Glaucoma (n = 41) No Self-Reported Glaucoma with Clinical Diagnosis of Glaucoma (n = 111) No Self-Reported Glaucoma without Clinical Diagnosis of Glaucoma (n = 1857)
Calcium
 No intake 49.9 25.9 50.5 48.3
 1st Quintile, >0 and ≤100 mg/day 4.5 27.7 7.9 12.0
 2nd Quintile, >100 and ≤200 mg/day 6.6 2.6 14.1 11.5
 ≥3rd Quintile, >200 mg/day 39.0 43.8 27.5 28.3
Iron
 No intake 74.4 76.3 83.4 78.7
 1st Quintile, >0 and ≤6 mg/day 0 3.3 1.2 4.5
 2nd Quintile, >6 and ≤15 mg/day 3.8 1.5 5.1 5.2
 ≥3rd Quintile, >15 mg/day 21.7 18.9 10.3 11.7
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×